Laminated glass panels in combination with timber frame as a shear wall in earthquake resistant building design

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1 See discussions, stats, and author profiles for this publication at: Laminated glass panels in combination with timber frame as a shear wall in earthquake resistant building design Conference Paper June 2012 CITATION 1 READS authors, including: David Antolinc University of Ljubljana 7 PUBLICATIONS 18 CITATIONS SEE PROFILE Roko Žarnić University of Ljubljana 41 PUBLICATIONS 348 CITATIONS SEE PROFILE Vlatka Rajcic University of Zagreb 73 PUBLICATIONS 158 CITATIONS SEE PROFILE Mislav Stepinac University of Zagreb 27 PUBLICATIONS 64 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: glued-in rods View project HISTCAPE View project All content following this page was uploaded by Mislav Stepinac on 08 July The user has requested enhancement of the downloaded file.

2 Challenging Glass 3 Conference on Architectural and Structural Applications of Glass, Bos, Louter, Nijsse, Veer (Eds.), TU Delft, June Copyright with the authors. All rights reserved. Laminated Glass Panels in Combination with Timber Frame as a Shear Wall in Earthquake Resistant Building Design David Antolinc, Roko Žarnić, Franci Čepon University of Ljubljana, Faculty of Civil and Geodetic Engineering, Slovenia, david.antolinc@fgg.uni-lj.si Vlatka Rajčić, Mislav Stepinac University of Zagreb, Faculty of Civil Engineering, Croatia, vrajcic@grad.hr The idea of the present study is to determine the in-plane stiffness and load bearing capacity of timber frame with laminated glass infill which acts as a shear wall and finally to estimate the contribution of such wall to the overall behavior of the entire building. For this reason we conducted an in-plane cycling load-displacement experiment of above mentioned wall system. The shear wall is composed of cross laminated timber frame and heat strengthened laminated glass panels, which are connected just with friction without any adhesives. The consequence of this type of connection is that we get larger displacements at a certain applied load which means higher ductility of the whole wall. On the other hand we get the problem to achieve the serviceability limit state. The comparison of the experimental results obtained for different types of timber frame connection details is made. The numerical simulation using ABAQUS software has also been done which gave us inaccurate results due to the inadequate timber frame connection modeling. The plan for the improvement of numerical modeling is made based on the additional experimental analysis of the timber frame elements connections. Keywords: Timber frame, laminated glass, dynamic load, seismic design, shear wall, in-plane stability. 2. Introduction There is no need for further discussion that glass is a unique material with its physical and mechanical properties as it has been proofed in many applications as the most competitive material. However, for the use of laminated glass in earthquake resistant building design it is important to consider the dissipation of energy at the structural level and the post fracture behaviour of the laminated glass itself. Considering architectural design of modern ground plan of any type of residential building where is the southern site of the building usually as transparent as possible and keeping all other sites with low percentage of the openings, we get the non-regular building in plan. This consequently means that such structures will show torsional behavior when exposed to the earthquake excitations. However, the current design philosophy considers the glass panels in glass facades as non-structural elements (EC8, Design of structures for earthquake resistant building design). This consequently means that we have to neglect these elements when designing the building resistance for the lateral load imposed by the earthquake. According to any modern design codes (e.g. EC8) it is necessary to design primary

3 Challenging Glass 3 d 0.005h structural elements within the limits of the prescribed story drifts ( r ) in order to protect non-structural elements. An important role in protecting of the nonstructural elements (glass façade panels) plays the connection detailing to the primary structural elements and the structural system of the façade itself. Commercially available curtain walls and façade panels can usually accommodate mm of elastic displacements, which is enough to sustain the displacements demand caused by the long term deflection, wind, thermal expansion, shrinkage and creep together with other movements that may arise during the service life of the structure [1]. During the event of the earthquake the façade glass panels face additional inelastic story drifts which can crucially impact the panels and consequently create life safety hazard. The mission of the present study is to show an innovative timber glass façade panels which can sustain larger story drifts and dissipate a considerable amount of energy during the event of the earthquake. Moreover, the idea is to show that such façade system can be even used as a primary (secondary) structural element and that it can take over some of the in-plane imposed load without creating life safety hazard. 3. Overview of the Specimens and the Racking Test Facility Three different types of specimens have been tested with racking test facility in our laboratory for three possible boundary conditions. The specimens are curtain walls assembled as a laminated timber frame with laminated glass infill. All three types of specimens are of the same geometry and dimensions (Figure 1) with different timber frame element connection details (CD1, CD2, CD3) in corners shown in the Figures 2a, b and c. Figure 1: Dimensions of the test specimens with the positions of the steel connections to the foundation and positions of the mesuring locations (SG1-12, LVDT0-10).

4 Laminated Glass Panels in Combination with Timber Frame as a Shear Wall in Earthquake Resistant Building Design Figure 2a, b and c: Connection detail of timber frame members with two bolts CD1 (a), one bolt CD2 (b) and one bolt with nail plate reinforcement CD3 (c). The glass panels with dimensions of 2900/2400 mm are made of two ply heat strengthened glass with thickness of 10 mm for one ply and 1.6 mm for EVA SAFE interlayer. As mentioned above is the assembly of each tested wall panel made of two just mentioned laminated glass panels which are tightly inserted into the timber frame and laterally closed with timber purlins attached to the main frame as shown in the Figure 3. The connection between timber frame and glass panels is ensured with friction only without any adhesives. Figure 3: Detailed view of the timber frame and laminated glass panels assembly Racking test set up In order to obtain the in-plane behaviour and the capacity of the considered shear wall panels the in-plane quasi-static racking tests were conducted in collaboration with the colleagues from the University of Zagreb. The racking test facility enables us to impose vertical load, which was 80kN ( 25kN/m) in our case and monotone horizontal as well as cyclic load H at the bottom of the panel. In the Figure 4 the setup of the racking test facility is shown where it is obvious that the specimen is fully restrained at the top into the reinforced concrete foundation strip while at the bottom of the specimen the boundary conditions can be changed (clamped, released rotation) which is shown in the Figure 5a, b, c.

5 F [kn] Story drift amplitude [mm] Challenging Glass 3 Figure 4: Quasi-static racking test facility. Figure 5a, b and c: Boundary conditions B1 of cantilevered panel (a), panel with restrained rotation at the bottom B2 (b) and with restrained vertical displacement and rotation at the bottom of the panel B3 (c). In the Figures 6a and b below it is shown the monotone load for the specimen FR3 and cycling story drift protocol for the specimen FR4 with boundary conditions B1 which is defined based on the monotone load according to the pren t [s] t [s] Figure 6a and b: Monotone load protocol (a) and cycling story drift protocol (b).

6 F [kn] Laminated Glass Panels in Combination with Timber Frame as a Shear Wall in Earthquake Resistant Building Design Ten quasi static racking tests have been conducted so far for the above mentioned wall panel specimens for different boundary conditions (BC1, BC2 and BC3), loads (monotone, cycling) and timber frame connections (two bolts, one bolt, steel nail plate with one bolt). In the next table 1 is shown which boundary conditions, loading protocol and timber frame connection details are attached to each of the wall panel specimens with designations from FR1 to FR10. Table 1: Boundary conditions, connection details and load protocol assignments to the specimens. Specimen FR1 FR2 FR3 FR4 FR5 FR6 FR7 FR8 FR9 FR10 Boundary conditions Connection detail Loading protocol BC1 BC2 BC3 CD1 CD2 CD3 Monotone Cycling 3.2. Friction force test setup and results For better understanding of the interaction between laminated glass panels and timber frame we conducted an additional experiment where we measured the friction force between glass and timber. The test setup is shown in the Figure 7a and as we can see it is assembled of one sheet of laminated glass which is embedded into two timber elements. For different levels (5 kn, 10 kn, 15 kn, 20 kn and 25 kn) of horizontal inplane compression applied loads we measured the force needed to push the glass ply in the vertical (perpendicular to the horizontal compression load) direction which represents the friction force. The result is friction coefficient (µ=0,15) between glass and timber which is further used for numerical modelling. The results for each of the inplane load levels are shown in the Figure 7b u [mm] 5 kn 10 kn 15 kn 20 kn 25 kn 30 kn Figure 7a, b: Friction force test setup (a) and relationship between friction force F and longitudinal displacements (b).

7 F [kn] Challenging Glass Buckling force test setup We also conducted the experiment to define the buckling force of the laminated glass panels used in the shear wall panels. The investigated glass panel is 2400 mm high and 1250 mm wide and it is inserted into the timber embedment on the top and bottom which is shown in the Figure 8. From the results of the test it is obvious that chosen type of the laminated glass panels (quality of the glass and interlayer) have relatively significant residual bearing capacity. This is also one of the reasons which encouraged us to use this type of laminated glass in a shear wall panels. Figure 8: Buckling force test setup. 4. Experimental results of the racking test Regarding to the data acquisition plan which is shown in the Figure 1 we have measured displacements (LVDT0-10) to capture the overall behaviour of the entire wall panel. We also measured strains (SG1-12) of the laminated glass panel at the certain locations to investigate the load transferring into the glass panel. In the next Figure 9 it is shown comparison of the displacements responses of the specimens FR3, FR7 and FR9 to the monotone load protocol at the story height (LVDT0) of the panel where each of the panels has different timber frame element connection detail and the same boundary conditions u [mm] FR3_B1_CD1 F7_B1_CD2 FR9_B1_CD3 Figure 9: Comparison of the displacement responses of FR3, FR7 and FR9 at the story level to the horizontal monotone applied load H.

8 F [kn] Laminated Glass Panels in Combination with Timber Frame as a Shear Wall in Earthquake Resistant Building Design From the comparison it is obvious that specimen FR3 which has frame elements connection detail with two bolts achieved the highest load bearing capacity which is due to the better stress distribution in the timber. The other two panels FR7 and FR9 both have timber frame connection detail with one bolt only where FR9 has additional reinforcement with the steel nail plate at the ends of the timber frame elements (in connections) to prevent splitting of the timber. We can see that wall panel FR9 shows more compliant behaviour comparing to the one without steel nail plate reinforcement FR7 but on the other hand the specimen FR9 shows more ductile behaviour and can achieve higher displacement level without total failure of the connection detail. Meanwhile the initial stiffness of all three specimens is similar for all specimens. Furthermore in the Figure 10 below it is shown the comparison of the wall panel displacement response to the imposed cycling load at the story height. The comparison is made for the specimens FR4, FR8 and FR10 which means that they have the same boundary conditions and connection details as the panels compared in previous figure 9. It is obvious that hysteresis of the specimen FR4 achieved the highest load bearing capacity where meanwhile the specimen FR10 with steel nail plate reinforcement achieved the highest displacements level. When comparing the dissipated energy the specimen FR8 has the lowest one which is a consequence of low or no contribution of timber frame connection after the early failure. The dissipated energies at the remaining two specimens are very close but it is necessary to expose that the frame connection at specimen FR10 stays relatively solid (because of the steel nail plate) at the end of the test which it is not true for the specimen FR u [mm] FR4 FR8 FR10 Figure 10: Comparison of displacement response of the wall panels FR4, FR8 and FR10 at the story height to the horizontaly applied cycling load H. 5. Future work We will continue with the experimental research of the wall panels with the CD2 and CD3 timber frame elements connection details for the remaining two boundary conditions (BC2, BC3) which have not been done to get the complete comparison of responses for all three connection details (CD1, CD2, CD3). These experimentally

9 Challenging Glass 3 obtained responses will also be modelled with the numerical simulation using ABAQUS software. We have tried to simulate the responses of already tested specimens with the mentioned software and we obtained inaccurate results mainly because of inadequate modelling of timber frame elements connections. In the Figure 11a it is shown the global meshed FE model in ABAQUS where 3D solid (C3D8I) finite elements were used together with general contacts to model the interactions between the wall panel elements. In the Figure 11b the closer view of the modelling for timber frame elements connection is shown. Figure 11a, b: Global meshed FE model (a) and closer view of the timber frame elements connection (b) modeled in ABAQUS. In order to improve the FE model we will conduct the experimental analysis of the timber frame elements connections separately to capture moment rotation and force displacement (modulus of slippage K ser ) behaviour and capacity which will enable us to prepare detailed FE model of the connection and then finally use it in the global model. However, there will be made the simulation of the whole building dynamic response based on the validated wall panel model to estimate the contribution of the considered wall panels to the safety of the entire building when exposed to the horizontal loads (earthquake). 6. Conclusions We can conclude that we get very ductile structural system with combining the timber frame and laminated glass infill. The results show us that the failure of the considered structural system appears at the timber frame elements connections. After the failure of the timber frame the friction force between glass panels and timber frame elements take over the imposed horizontal load. On the other hand we can conclude that timber frame represents the protection of the glass panels and the connection between glass panels and main structure, where even after the timber frame elements connections failure the vertical load still can be sustained. Thus, we can fulfil one of the main targets (philosophy) of any modern earthquake resistant building design codes which is to design buildings with some damage allowance but without catastrophic failure to protect the human lives.

10 Laminated Glass Panels in Combination with Timber Frame as a Shear Wall in Earthquake Resistant Building Design 7. Acknowledgements I would like to thank to the Slovenian research agency for funding of young researcher David Antolinc with the contract no /2008. I would also like to acknowledge the Ministry of science, education and sport of Croatia for funding the scientific project Characteristics of the composite structures wood structural glass and wood steel (leader Prof. Vlatka Rajčić). 8. References [1] McBean, Peter, Drift Intolerant Façade Systems and Flexible Shear Walls. Do we have a Problem?, Proceedings of the Annual Technical Conference of the Australian Earthquake Engineering Society Albury, Albury, NSW Australia, [2] Behr, Richard A, Architectural Glass for Earthquake-resistant Buildings, Proceedings of the 7 th international glass conference in Tampere (Glass Processings Days 2001), Tampere, Finland, [3] Pantelides, C. P., Truman, K. Z., Behr, R. A., Belarbi, Development of a Loading History for Seismic Testing of Architectural Glass in a Shop-front Wall System, Engineering Structures, 1996, Vol. 18, No 12, pp [4] Huveners, E.M.P., Herwijnen, F., Soetens, F., Hofmeyer, H., In-plane loaded glass pane (shear wall), Proceedings of the 10 th International Conference in Tampere (Glass Performance Days), Tampere, Finland, [5] Mocibob, Danijel, Glass Panel under Shear Loading Use of Glass Envelopes in Building Stabilization, PhD thesis, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland, [6] Freitag, Claudia, Woerner, Johan-Dietrich, Glass as structural bracings shear capacity of mechanically pre-stressed windowpanes, Glass Performance Days 2009 Proceedings (Proceedings of the 11 th international conference), Tampere, Finland, [7] Sucuoglu, Haluk, Vallaghan, C. V. Girja, Behaviour of window glass panels during earthquakes, Engineering Structures, 1997, Vol. 19, No 8, pp [8] Sivanerupan, S., Wilson, JL., Gad, EF., Lam, NTK., Seismic Assessment of Glazed Façade Systems, Proceedings of the Annual Technical Conference of the Australian Earthquake Engineering Society, Newcastle, NSW Australia, [9] Niedermaier, P., Shear-strength of Glass Panel Elements in Combination with Timber Frame Constructions, Glass Processing Days 2003 Proceedings (Proceedings of the 8 th international conference), Tampere, Finland, [10] Memari, Ali M., Shirazi, Ali, Kremer, Paul A., Behr, Richard A., Development of Finite-Element Modeling Approach for Lateral Load Analysis of Dry-Glazed Curtain Walls, Journal of Architectural Engineering, 2011, Vol. 17, No 1. View publication stats